1. Field of the Invention
The present invention relates to an ink jet printing apparatus that forms an image on a printing medium by using a print head capable of ejecting ink from its ejection openings. The invention also relates to a device and a method to recover a performance of the print head.
2. Description of the Related Art
Ink jet printing apparatus have many advantages, such as a relative ease with which a print head can be reduced in size, an ability to print a high resolution image at high speed, an ability to print on plain paper without having to apply a special treatment to it, a low running cost, low noise realized by a non-impact printing, and an ease with which color images can be printed using multiple color inks. A bubble jet (trademark) print head that utilizes thermal energy in ejecting ink, in particular, can easily be reduced in size. By taking advantage of features of IC and microfabrication techniques, this type of print head can easily be manufactured in an elongated form, a two-dimensional form or a full multi-type form, and also in a high density construction.
Among such bubble jet (trademark) print heads are an edge shooter type print head that ejects ink parallel to a heater board incorporating electrothermal transducers and a side shooter type print head that ejects ink in a direction perpendicular to the heater board. In the side shooter type print head, an electrical connection portion between a print chip and an electric wiring member is provided on a face of the print head (a surface in which ink ejection openings are formed). The print chip is a nozzle plate formed by the above-mentioned fabrication process using the IC or microfabrication technologies. The electric wiring member may be, for example, a TAB to send a signal from an ink jet printing apparatus to the print chip. The electrical connection portion needs to be sealed with a sealant of resin or the like that is impervious to ink and electrically non-conductive.
Among the ink jet printing apparatuses, there is a serial scan type printing apparatus which forms an image by reciprocally moving the print head over print paper (printing medium) with a small gap therebetween and at the same time ejecting ink droplets from ejection openings of the print head onto the printing medium. As the image forming is performed by reciprocally moving the print head, foreign matters such as viscous ink, dirt and paper dust may adhere to the face of the print head, interfering with a stable ink ejection operation. To prevent a possible printing failure due to the adhesion of foreign substances and to improve a printing performance, a cleaning means is used to remove the adhering foreign substances from the print head. This cleaning means wipes the face of the print head with, for example, a wiper blade of an elastic rubber member such as urethane rubber to remove the foreign substances.
Such a conventional technology is disclosed, for example, in Japanese Patent Application Laid-open No. 7-237301(1995).
Generally, in a print head using a pigment ink, it is known that the wiping operation for removing the remaining pigment ink off the face of the print head can, after having been repeated a large number of times, degrade a water repellency of the print head face. Once the water repellency of the print head face deteriorates, the wiping operation may not be able to wipe the face clean, leaving the pigment ink on the face. If the print head in this condition ejects ink from its ejection openings, an ink droplet being ejected is pulled by the residual ink near the ejection opening, with the result that the ink droplet may not be projected in the normal direction and land at a deviated position on a printing medium. This in turn may cause density variations of a printed image in the form of light or dark lines, degrading a print quality.